Rivnuts from Homestead,PA on 7/7/2023 11:28:26 AM:
If you are starting in Pittsburgh, consider Golden Triangle Bikes at (412) 600-0675.
They are located right on the GAP Trail about 1/2 mile from Point State Park which is the terminus of the GAP Trail in downtown Pittsburgh. You may be able to rent a bike from them in DC as well, but I don’t have any specific information to do so.
PS: I have no personal stake in this shop whatsoever.